The present invention relates to an abrasive material having an abrasive layer of a three-dimensional structure, and more particularly to an abrasive material having an abrasive layer of a three-dimensional structure and being suited for abrading an end surface of an optical fiber on which a ferrule is mounted, i.e., an end surface of an optical fiber connector, into a predetermined shape.
Conventionally, an optical fiber connector which can be easily removed is widely used for connection of optical fibers in an optical fiber communication network. In the connection at the optical fiber connector, end surfaces of the optical fiber ferrules made of an optical fiber and a covering portion (ferrule) for covering the optical fiber are allowed to directly abut each other. Therefore, the optical characteristics at the time of connection, particularly the connection loss, depend on the processing properties and precision of the end surfaces of the optical fibers.
The end surface of the optical fiber ferrule is processed through a number of abrasion steps. The quality of the end surface is influenced by the processing properties and the precision in the final finishing abrasion step. In other words, the major factors for the connection loss of the optical fiber are the degree of finishing roughness of the end surface and its inclination.
With respect to the finishing roughness of an end surface of an optical fiber ferrule, correlation with the particle size of an abrasive material used for the abrasion is reported. For example, in the case of a step index type fiber, the connection loss is about 0.5 dB if the particle size of the abrasive grains is about 1 xcexcm whereas the connection loss is more than about 1.0 dB if the particle size of the abrasive grains is about 15 xcexcm.
Upon observation of this correlation, it will be under stood that abrasive grains having a particle size of 10 to 15 xcexcm must be used in order to satisfy a standard requiring the connection loss of the optical fiber to be less than 1 dB, and fine grade abrasive grains having a particle size of less than 1 xcexcm must be used in order to satisfy a standard requiring the connection loss of the optical fiber to be less than 0.5 dB.
Japanese Laid-open Patent Publication No. 09-248771/1997 discloses an abrasive tape for an end surface of an optical fiber connector in which the abrasive tape has a base material and an abrasive layer disposed on the base material, the abrasive layer is composed of silica particles having an average particle size of 5 to 30 xcexcm and has a binder for connecting these abrasive material particles, and the central line average roughness Ra of the abrasive layer surface is 0.005 to 0.2 xcexcm.
Fine grade abrasive materials such as an abrasive tape for an end surface of an optical fiber connector have a problem of loading. The term xe2x80x9cloadingxe2x80x9d means that the space among abrasive grains is filled with abrasion dusts that protrude to inhibit the abrasive property. For example, in the case where an end surface of an optical fiber connector is abraded, the particles of abrasion dusts stay in the space among the abrasive grains, whereby the cutting ability of the abrasive grains decreases. Further, liquid that is used as a coolant and a lubricant does not act sufficiently between the abrasive material and the end surface of the optical fiber connector, whereby a part of the abrasive layer adheres to the surface of the optical fiber connector after abrasion and its removal is cumbersome.
Moreover, if fine particles are used as the abrasive grains, the period of time required for abrasion will be long. On the other hand, if the particle size of the abrasive grains is increased, the finished end surface of the optical fiber connector will be rough, thereby failing to meet the standard for connection loss of the optical fiber. If both methods are used in combination, the number of abrading steps will increase.
WO92/13680 and WO96/27189 disclose an abrasive material having an abrasive layer of a three-dimensional structure. This abrasive material has a base material and an abrasive layer disposed on the base material, the abrasive layer is made of an abrasive composite containing abrasive particles and a binder, and the abrasive layer has a three-dimensional structure constructed with a plurality of regularly arranged three-dimensional elements having a predetermined shape. As the shape of the three-dimensional elements, tetrahedral shape, pyramidal shape, and others are disclosed.
This abrasive material is resistant to loading and excellent in durability. However, since the abrasive grains are uniformly dispersed all over in the abrasive layer and the abrasive grains located on the lower part of the abrasive layer do not act effectively, the production cost is high.
Further, an abrasive material having such an abrasive layer of a three-dimensional structure is produced by applying an abrasive slurry containing abrasive particles and a binder in a mold sheet having a structure, superposing a base material on the mold sheet to bond the binder to the base material, hardening the binder by ultraviolet radiation, and removing the mold sheet. In this case, the abrasive slurry must have a sufficient fluidity to be introduced into the structure within the mold sheet. Further, since the ultraviolet radiation is performed after covering the abrasive slurry with the base material, the abrasive slurry must not contain a volatile component.
Therefore, the content of the abrasive grains in the abrasive slurry cannot exceed the critical pigment volume concentration. Accordingly, the conventional abrasive material having an abrasive layer of a three-dimensional structure has a problem that the content of abrasive grains in the abrasive layer cannot be sufficiently raised.
By comparison under abrasive conditions in which the particle size of abrasive grains, the abrasive means, and others are the same, the abrasive property of the abrasive material will decrease as the content of the abrasive grains is reduced. Particularly, in fine grade abrasive materials, the abrasive efficiency will be poor to increase the period of time required for abrasion if the content of the abrasive grains is insufficient.
Accordingly, since the content of the abrasive grains is insufficient, the conventional abrasive material having an abrasive layer of a three-dimensional structure is poor in abrasive property and hence is not suited for abrading a hard material such as an end surface of an optical fiber connector efficiently and smoothly into a predetermined shape.
The present invention has been made to solve the aforesaid problems of the prior art and an object thereof is to provide an abrasive material which is excellent in loading resistance and durability, allows no attachments to attach to an abraded surface even when the end surface of the optical fiber is abraded, and is particularly suited for use in abrading a hard material such as an end surface of an optical fiber connector effectively and smoothly into a predetermined shape.
The present invention provides an abrasive material for abrading an end surface of an optical fiber connector into a predetermined shape, the abrasive material having a base material and an abrasive layer disposed on the base material, the three dimensional elements having (1) top layer comprising an abrasive composite comprising abrasive grains dispersed within a binder and (2) a foot portion comprising a binder in the absence of abrasive particles, the abrasive layer having a three-dimensional structure constructed with a plurality of regularly arranged three-dimensional elements having a predetermined shape, thereby to achieve the aforesaid object of the present invention.
Further, the present invention provides a method for producing an abrasive material having an abrasive layer of a three-dimensional structure, the method comprising the steps of: (1) filling a mold sheet having a plurality of regularly arranged recesses, with an abrasive material coating solution containing abrasive grains, a binder, and a solvent, to a predetermined depth; (2) removing the solvent from the abrasive material coating solution in the recesses by evaporation; (3) filling the recesses further with a binder in the absence of abrasive particles; (4) laminating a bass material on the mold shoot to bond the binder to the base material; and (5) hardening the binder.
The abrasive material having an abrasive layer of a three-dimensional structure is preferably produced by the aforesaid production method.